Calcaire à cératites
The Calcaire à cératites is a sedimentary formation of the eastern Paris basin . It was deposited in the Upper Muschelkalk during the Triassic period .
etymology
The Calcaire à cératites, in German Ceratitenkalk or Ceratitenschichten , is derived from the French. calcaire (lime) and the ammonite order of the ceratites (French cératites ).
Occurrence
The Calcaire à cératites is mainly in the eastern Paris basin . It follows the upper section of the Muschelkalkband from southeast Luxembourg via Faulquemont , Sarreguemines , Sarrebourg , Vittel to Corre to the southern edge of the Vosges . In Germany, the Calcaire à cératites occurs in Bliesgau .
stratigraphy
The Calcaire à cératites follows concordantly on the Calcaire à entroques and is in turn superimposed concordantly by the Calcaire à térébratules . Its thickness varies between 45 and 50 meters. The clearly layered formation consists lithologically of an alternation of 20 to 30 centimeters thick, light gray, fine-grained, platy limestone banks and 10 to 20 centimeters thick, dark gray clay - marly intermediate layers .
A typical alternation is a total of 30 centimeters (up to a maximum of 50 centimeters) thick. It begins with a bioclastic lime about 10 centimeters thick made up of fossil remains (shell and sea lily remains ) and micritic intraclasts . The basis is erosive in nature and the intraclasts carried along come from the reprocessing of the previous sequence. After the clay / marl layer, which is 15 centimeters thick, a very fine-grained microbank of 5 centimeters follows. This micrite has been precipitated chemically. The sequence then ends with a more or less wavy layer gap (diastema).
Fossils
The limestone banks are often traversed by corridors and buildings of sediment dwellers. The eponymous Ceratites are represented in the lower 35 to 40 meters by Ceratites nodosus , in the upper 10 meters by Ceratites semipartitus . Remains of Myophoria , Gervillia , Ostrea , Pecten , Lima and Coenothyris are much more numerous . Some hanging benches also contain terebratels .
The presence of ammonites clearly demonstrates marine conditions (but not necessarily deep water) for the Calcaire à cératites. The Muschelkalkmeer had reached its highest level at this time.
Age
Absolute ages are not available for the Calcaire à cératites. However, based on the fossils and its biostratigraphic position shortly before the end of the Upper Muschelkalk, it can be assigned an age of around 236 million years BP ( Ladinium ).